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School entry age may impact risk of ADHD diagnosis

The age at which a child starts school may influence their likelihood of being diagnosed with attention deficit hyperactivity disorder, suggests a new study published in The Journal of Pediatrics.

ADHD is one of the most common disorders of childhood.

Attention deficit hyperactivity disorder (ADHD) is estimated to affect around 6.4 million children aged 4-17 in the US, making it one of the most common childhood conditions.

ADHD is characterized by poor attention, hyperactivity and impulsive behavior. It is most commonly diagnosed at the age of 7, and boys are more likely to be diagnosed with the condition than girls.

The causes of ADHD remain unclear, though some studies have suggested that it may be down to genes, use of alcohol, cigarettes or drugs during pregnancy, exposure to environmental toxins - such as lead - at a young age or brain injury.

Now, Dr. Mu-Hong Chen, of the National Yang-Ming University in Taipei, Taiwan, and colleagues suggest a diagnosis of ADHD may be related to the age at which they start school.

Risk of ADHD diagnosis higher in August-born schoolchildren

To reach their findings, the team analyzed 1997-2011 data involving 378,881 children aged 4-17 years.

Fast facts about ADHD

Between 2003-2011, the number of children diagnosed with ADHD in the US increased from 7.8% to 11%

Boys are more than twice as likely to be diagnosed with ADHD than girls

Children with a history of ADHD have almost three times as many peer problems as those without a history of ADHD.

The researchers assessed the prevalence of ADHD diagnosis among the children and whether they were prescribed medication for the condition.

They also looked at what age the children were enrolled in school, taking into account the annual cut-off date for school entry in Taiwan: August 31st.

The team compared ADHD prevalence and medication prescription among the youngest children in a grade (those who were born in August) with the older children in a grade (those born in September).

The researchers found that preschool and elementary school children born in August were more likely to be diagnosed with ADHD and receive medication for the disorder, compared with those born in September.

Adolescents who were born in August, however, were at no higher risk of an ADHD diagnosis than those born in September.

"This result may imply that as age and maturity level increased in teenage years, the influence of birth month would have less of an impact on ADHD diagnosis and treatment," say the authors.

This prompts the question: are many schoolchildren being misdiagnosed with ADHD because they are displaying immature behaviors relative to their older classmates?

Commenting on their results, the researchers say:

"Relative age, as an indicator of neurocognitive maturity, may play a crucial role in the risk of being diagnosed with ADHD and receiving ADHD medication among children and adolescents.

Our findings emphasize the importance of considering the age of a child within a grade when diagnosing ADHD and prescribing medication to treat ADHD."

Influence of relative age on diagnosis and treatment of attention-deficit hyperactivity disorder in Taiwanese children, Mu-Hong Chen et al., The Journal of Pediatrics, doi: 10.1016/j.jpeds.2016.02.012, published online 10 March 2016, abstract.

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